A strong signal can fill a loudspeaker and still fail to produce the right action. Maritime communication succeeds only when the receiver identifies, interprets and can use the message.
Signal strength is only the first layer
Radio equipment can indicate that energy is reaching the receiver. That says little about whether words were separated correctly, numbers were copied accurately or the intended station realised the call was for it. Interference, competing transmissions and background noise can preserve volume while destroying meaning.
The listener brings a mental model
People do not hear speech as neutral data. They predict words from context. This usually makes conversation efficient, but it can produce confident errors. Research on pilot–controller radio communication puts it bluntly: “we are predisposed to hear what we expect to hear,” and similar call signs on the same frequency were the most common factor found alongside miscommunication.1,2 At sea, an unfamiliar vessel name may be replaced mentally by a familiar one. A latitude, channel or time can be heard as the value the listener expected.
Accents and language differences add variation, but the problem is not simply “poor English.” ICAO’s guidance on language proficiency in aviation stresses that native English speakers “have a fundamentally important role to play” in communication safety too.3 Standardised words and spelling conventions help by reducing the number of plausible interpretations; the IMO Standard Marine Communication Phrases prescribe both a spelling alphabet and the pronunciation of digits.4
Understanding must lead to action
A report such as “we have a problem near the harbour” may be audible and linguistically clear, yet still leave a coordinator unable to task a suitable response. Actionable information connects the event to identity, location, time, nature of difficulty and people at risk—the same elements that structure a distress message: identity, position, nature of distress, assistance required and persons on board.5
Conversely, too much unstructured detail can hide the critical facts. Good operational communication is not the longest message. It gives the receiver enough verified information to decide what happens next.
Readback closes the loop
Repetition and readback reveal differences between what was sent and what was received. They are especially valuable for positions, channels, times and instructions. The SMCP gives the speaker a tool for this: “Repeat …” followed by the part of the message that needs safeguarding.4 A sender who hears an incorrect readback can repair the error before it becomes part of the operational picture.
But readback only works if someone listens to it. In one FAA study of tower communications, controllers failed to notice the error in more than a third of incorrect readbacks.1 Hearing the readback is part of the job.
This closed loop is a human reliability tool. It matters whether the link is analogue voice, a telephone call or follow-up to a digital alert.
The environment speaks too
Wind, engines, alarms, breathing apparatus and vessel motion compete for attention. Microphone distance, speech pace and the physical effort of the speaker change intelligibility; radio manufacturers advise holding the microphone about one inch from the mouth and speaking in a normal voice to avoid distortion.6 At the receiving end, workload and multiple simultaneous calls determine how much information can be processed.
A shared responsibility
The sender is responsible for clarity, but the receiver must signal uncertainty and seek confirmation. Organisations also shape the outcome through equipment, training, channel management and staffing. Communication failure is rarely explained by one person’s voice alone.
Being heard is a technical event. Being understood is a joint operational achievement.
Sources and further reading
- Cardosi, K. M. (1994). An analysis of tower (local) controller–pilot voice communications. DOT/FAA/RD-94/15. U.S. Department of Transportation, Federal Aviation Administration.
- Monan, B. (1991). Readback/Hearback. ASRS Directline, Issue 1. NASA Aviation Safety Reporting System.
- ICAO. Manual on the Implementation of ICAO Language Proficiency Requirements, Doc 9835. Quoted in SKYbrary: English language proficiency requirements.
- IMO (2001). IMO Standard Marine Communication Phrases, Resolution A.918(22). See also IMO: Standard Marine Communication Phrases.
- Maritime and Coastguard Agency (2024). GMDSS VHF DSC procedures for small boat users.
- Icom UK. How to use a Marine VHF Radio.
- ITU-R Recommendation M.1171-1 (2023). Radiotelephony procedures for routine calls in the maritime mobile service.
- International Maritime Organization. Human element.
Editorial note: This article discusses human factors and does not replace prescribed radiotelephony procedures or approved training. Last fact-checked: 3 October 2026.
